The present invention relates to a water quality meter to measure the quality of drinking water distributed via pipes and a water quality monitoring system using the water quality meter.
As an example of a water quality monitoring system, an automatic water quality measurement system known to be used in Tokyo, and its design specification is described in a paper of The Journal of The Society of Instrument and Control Engineers (Japan), Vol. 33, No. 8, August 1994, pp. 649-653.
In this water quality measurement system, a water quality meter is provided at each of the piping subsystems composing a water supply piping network at a water supplier, and it continuously measures the water quality of each piping system. Furthermore, the measured water quality is transmitted to a control center with a telemeter at regular intervals.
As a means for measuring the water quality for end users, a manual analysis in which the distributed water of the end user is sampled and manually analyzed with a reagent or an off-line measurement using a portable water quality meter is performed.
In a conventional water quality monitoring system such as the above-mentioned system, since a water quality meter is provided in each water piping subsystem, the number of the provided meters is comparatively small, and the average quality of water distributed in each subsystem can be determined. However, the conventional system has a problem in that the quality of water which end users drink is not determined.
The quality of water is measured and controlled at a water supplying facility. However, the water quality is degraded while water passes through a water distribution piping network. For example, the concentration of chlorine to maintain the bactericidal activity in drinking water is decreased due to chemical reactions with the materials composing the water distribution system or with components contained in the drinking water. Also, the chromaticity of drinking water is increased by coloring due to stains on the inside surfaces of the pipes, and the turbidity of drinking water is also increased due to the peeling of deposits on the inside surfaces of the pipes. Although the above-mentioned degradation of water quality is naturally caused in main pipes, this degradation is more strongly caused in end side pipes in a water distribution piping network or in pipes in the houses of end users. It is well known that the concentration decrease of residual chlorine in water is proportional to the staying time in water. The staying time of chlorine in water is longer in the end side pipes than in the main pipes in which water always flows. Therefore, the concentration of residual chlorine is decreased in the end side pipes. Furthermore, in the extreme case, the concentration of chlorine becomes zero, and water without the bactericidal activity may be drunk. The concentration decrease of residual chlorine causes the degradation of the bactericidal activity of water, which may cause the breeding of microbes, and especially of pathogenic microbes (for example, O-157 coliform bacilli), and further cause a social problem concerning the safety and health of people. On the other hand, increasing the concentration of chlorine in drinking water to a higher level to maintain the bactericidal activity of drinking water causes the problem of a bleaching powder smell or a safety problem of producing harmful substances such as a chloric residuum of trihalomethane.
As to the chromaticity and the turbidity of drinking water in the end side pipes also, problems similar to the above-mentioned problems are caused due to the long staying time of water. In particular, a water storage tank is used in aggregate residences or business establishments, and if the water storage tank is not well managed, the above problems are often caused.
In an ideal water quality management system, the quality of water in the end side pipes, which end users drink, is monitored, and is adequately managed based on the results of the monitoring. The size of a conventional water quality meter, for example, 1.2 m.times.1.8 m.times.0.6 m, is so large that it cannot be provided in places such as a typical house or aggregate residences. Since the price of a conventional water quality meter or the cost of providing a conventional water quality meter is high, the number of conventional water quality meter provided in typical houses or aggregate residences is small. Furthermore, since professional expertise is required for the maintenance of a conventional water quality meter and the consideration for the safety of a meter is important, it is difficult to use a conventional water quality meter in typical houses. Thus, conventional water quality meters have not been provided at a desirable pipe location in the neighborhoods of houses of end users or of aggregate residences.
On the other hand, although the quality of water at the end side of a water distribution piping network can be measured by a manual analysis or with a portable water quality meter, it takes a long time for measuring results to be obtained, and water quality data cannot be continuously obtained, which makes it impossible to determine the range of variation in water quality in a day, or the transient behavior of water quality.
In water quality data, the maximum and minimum values in a transient state are important, and the development of a system and a control method of the system to reduce the variation in these values is mandatory. Therefore, a manual analysis or a portable water quality meter is not suitable for the above continuous monitoring system.
In a very rare example, by restricting measurement categories and places in which water quality detectors are provided, for example, by providing residual chlorine concentration detectors at the rate of one per ten to thirty-plus thousand end users at end side pipes of a water distribution system, an on-line water quality measurement has been performed. However, conventional water quality meters used in the above water quality measurement can measure only one category, and are also large and expensive meters similar to ones used in water purifying facilities. Therefore, places in which such meters are set cannot be easily obtained, and it is also to difficult to obtain sufficiently detailed measurements of water quality.